421 email error is typically a temporary routing issue on the receiving mail server's end. These should usually be resolved automatically, and you should receive a final bounce-back message if the message completely fails.

You usually would not receive a bounce-back message for this type of error. If your message is going to be delayed more than 24 hours, then sometimes a "delivery has been delayed" soft bounce will be returned to you, to let you know that the delivery has yet to complete succesfully.

Common variations of the 421 email error

  • 421 4.2.1 : (DYN:T1) http://postmaster.info.aol.com/errors/421dynt1.html
  • 421 4.3.1 Out of disk space for temp file
  • 421 4.3.2 All server ports are busy
  • 421 4.3.2 All server ports are busy
  • 421 4.4.2 mx.aol.com Error: timeout exceeded
  • 421 #4.4.5 Too many connections from your host.
  • 421 #4.4.5 Too many connections to this host.
  • 421 4.7.0 mx.aol.com Error: too many errors
  • 421 4.7.1 : (DYN:T1) http://postmaster.info.aol.com/errors/421dynt1.html
  • 421 4.7.1 POL-T2 http://postmaster.facebook.com/response_codes?ip= Connection refused
  • 421 4.7.1 POL-T2 http://postmaster.facebook.com/response_codes?ip= Connection refused

  • 421 Downstream server error
  • 421 Fork failed
  • 421 Greylisting enabled, please try later.
  • 421 LDAP verification agent temporarily unavailable: Connection failed
  • 421 mail.RemoteDomain.com out of connection slots
  • 421 mx.aol.com Service unavailable - try again later
  • 421 <recipient@RemoteDomain.com> Service not available - too busy
  • 421 Server busy, try again later - psmtp
  • 421 service temporarily unavailable
  • 421 Temporary error (#4.3.0)
  • 421 Too many concurrent SMTP connections; please try again later.
  • 421 Unexpected failure, please try later

Resolving a 421 email error

Because errors in the 421 series don't bounceback right away they would be considered a soft bounce. To better understand soft and hard bounces, and general email bounceback errors you can read why does email bounce, bounceback, or error?

Seeing a large amount of 421 email errors in your server's mail logs could be an indication that a lot of your mail users are having difficulties getting their e-mails delivered out successfully on the first attempt.

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n/a Points
2014-05-29 1:56 pm

I keep getting "too many simultaneous connections" for my AOL account. I have a multitude of phones, tablets, and computers that have my AOL account attached. Is there a limit to how many "connections" I can have? If so< what is my next step? If not. how to I remedy this?



9,968 Points
2014-05-29 3:59 pm
Hello Kady, and thanks for your comment.

Are you getting this error just when trying to send email to an AOL email account? This guide itself is on 421 errors, and you would typically see it in a bounce-back message after a message you sent to a AOL user failed to send. In this case you would want to try to send the message again at a later time as the AOL server could be temporarily overloaded.

If you are just getting this error in your mail client, and you are using your AOL account in multiple devices at once, you might be having an issue with IMAP usage on their server.

You might need to stagger the times your different devices check your mail. For instance, have your phone check every 5 minutes, tablets every 7 minutes, first computer every 9 minutes, and so on. You might also want to reduce the total number of messages stored in your main Inbox folder, and archive away messages you don't need to access often. Some email clients will tie up IMAP connections by trying to download lots of old message headers from the server for a message that's older than 30 days and you might not be reading anyways.

Hope that helps, please let us know if you still have any questions at all!

- Jacob

n/a Points
2014-07-31 5:28 am

I am getting 421 error - too many messages? what does that mean. also I am getting a grey pop up box that says do you want to save this password in the list, everytime I send sonmeone an email, what does that mean?I am able to send and receive emails OK, just these annoying two pop up boxes that wont go away. please help

18,017 Points
2014-07-31 9:21 am
This error is typically from the receiving server so it should not be a result of your account. It seems that the receiving server may be getting more mail than it is set to expect, so it is giving the "too many messages" message. You may want to try resending the email again at a later time to see if it will accept it.

Kindest Regards,
Scott M
n/a Points
2014-07-31 10:10 am

this has been happening for about a week now. I send lots of mail and have done for years but I am only getting these error messages for the past week.

the worst pop up box is the grey one that says do you want to save this password in the list, it pops up every two seconds, it is so annoying. i dont know what to do about it.

I am not at all technical and I dont have anyone that can help me :(

8,314 Points
2014-07-31 10:29 am
Are you sending multiple messages in succession to the same email address or to a bulk mailing list?
n/a Points
2014-07-31 10:34 am

different email addresses. similar messages - as I work for a charity and I send membership packs by email. I have been using outlook 2007 to do this for years and only now is it a problem

8,314 Points
2014-07-31 10:38 am
How big is the mailing list? Are you sending them all at once? A specific service provider is most likely seeing a lot of messages coming in to their users and blocking based on that to prevent spam.
n/a Points
2014-08-01 5:55 am

I am getting the error accompanied by an Unexpected log failure

Can anyone please help me>

8,314 Points
2014-08-01 9:15 am
Could you provide us with the exact error that you are getting?
n/a Points
2014-08-27 2:26 am


I am getting an error when I am trying to send emails to some domains(ocscmb.com, falco.lk).

This is the mail system at host relay.mailchannels.net.


I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.


For further assistance, please send mail to postmaster.


If you do so, please include this problem report. You can delete your own text from the attached returned message.


                   The mail system


<ruvi.wijemuni@ocscmb.com>: host mx07.register.com[] refused to

    talk to me: 421 Downstream server error


The error I am getting is in bold above. Please explain me the reason and a solution for this.


Thank you very much.

8,314 Points
2014-08-27 11:16 am
It appears that the remote mail server that you are sending to is closing the connection. Unfortunately, as their mail server is outside of our network, we do not have the specific reasoning as to why. For this, I recommend speaking with the individual that you are attempting to send to by other means to identify what on their server may be causing the issue.
n/a Points
2014-08-27 10:41 pm

Hi JrffMa,

Thanks, sure...will try to do that...

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